Direct reading radio navigation receiver



J. T. McLAMoRE ET AL 2,487,822

5 Sheets-Sheet l Nav. 15, 1949 DIRECT READING RADIO NAVIGATION RECEIVER Filed April so, 1947 Nov. 15, 19,49 .1.1'. McLAMoRE ETAL 2,487,822

DIRECT READING RADIO NAVIGATION RECEIVER INVENTOR.

i H John 'IlMcLamore, Milton J.Mnne'man and TealE.Dunn

ATTORNEY Nov. l5, 1949 J. T. McLAMoRE ErAL 2,487,822

DIRECT READING RADIO NAVIGATION RECEIVER i n L V #VI V1 i F Wil-7x50 /Noex MARKER VAR/ABLE wasx MARKER ,l ,l/ w]- f l d' e Hl L 2 c a X@ INVENTOR. Jhn' T. McLmore, F 4 Milon J. Mmnernan r /lg' and Ted E.Dunn

BY @M A .UFCNEY Nov. 15, 1949 J. r. McLAMoRE ETAL DIRECT READING RADIO NAVIGATION RECEIVER Filed April 5o, 1947 5 Sheets-Sheet 4 Nov. 15, 1949 .1.1. MCLAMQRE Erm. 2,487,822

DIRECT amine nAnIo uAvIGA'rIon RECEIVER Filed April 30, 1947 5 Sheets-Sheet 5 FAST SWEEP CIRCUIT lNvENToR. John" T.McLamore, Milton J.Minneman, and Ted E.Dunn' l l l l I l l Patented Nov. 15, 1949 DIRECT READING RADIO NAVIGATION RECEIVER John T. McLamore, Haddoniield, Milton J. Minneman, Camden, and Ted E. Dunn, Pennsauken,

Y N. J., asslg'nors torRadio Corporation of America, a corporation of Delaware i' Application April 30, 1947, Serial No. 745,028

9 Claims. f l Our invention relates to radio navigation systems and particularly to systems of the type utilizing the time difference in the propagation of radio pulses from synchronized ground stations. -Navigation systems of this type employ pairs of. synchronized ground transmitting stations that emit radio pulses having a xed time relation. Each pair of ground stations preferably transmits pulses at an assigned individual repetition rate for the purpose of station selection. The pulses are broadcast so that they may be received by means of equipments located in the aircrafts or ships whose positions are to be determined. By means of the receiving equipment, the operawr on the craft determines the time difference between the pulses from the two transmitter stations of one pair as they arrive atthe receiver. Since the radio pulses travel from the ground transmitters to thereceiver at a known propagation rate (i. e. atthe velocity of light), it is known that the position of the craft is at some point on a line corresponding to the time difference reading. By obtaining the time difference reading from a second pair of ground stations, a second line corresponding to the second time difference reading is obtained, and the intersect point of the two lines is the position of the craft. Special maps having the time difference lines printed thereon for the several pairs of Vground stations are provided for use with the navigation system. l

In order to measure the time difference in the arrival of successive pulses from a pair of ground stations, the receiving equipment is arranged to generate pulses at selected repetition rates. The pulses may be adjusted to have a definite time relation to-the time of arrival of the ground station pulses and are provided for the purpose of driving or synchronizing cathode-ray deflecting circuits. Thedetlecting circuits produce cathode-ray sweep traces on which the received ground station pulses are displayed.

For the purpose of selecting a, particular pair of ground stations, the operator selects the particular pulse repetition rate for the driving or synchronizing pulses corresponding to the repetition period of the pulses transmitted from said pair whereby the deflecting circuits may be synchronized with the received pulses from the selected pair of ground stations. Thus a particular pair of ground stations is selected at the receiver apparatus by turning a. station selection switch to the position indicated on the receiver panel for obtaining sweep synchronizing pulses having the 2 ing transmitted from the selected pair of ground stations. Now the received pulses from the selected pair of ground stations can be made to appear stationary on the cathode-ray sweep or trace whereas those received from the other pairs of ground stations will move along the same race.

The pulses from the two transmitter stations of a selected pair will be referred to as A and B pulses, respectively, and the B pulse is identied vin the present system as the pulse that occurs after or follows the mid-point of the other pulse period. In operation, the A and B pulses are displayed, respectively, first on two slow-sweep cath- I ode-ray traces and then on two fast-sweep cathode-ray traces, thereby enabling the operator to adjust a plurality of delay or phase shift circuits so that the time difference between the pulses driving or synchronizing the 'cathode-ray d eilecting circuits equals exactly the time diierence between A and B pulses.

The adjustment for the display and alignment of the A and B pulses is accomplished by rst setting the A puise at the left end of the upper slow-sweep trace, when the receiving apparatus is switched to an operating position marked #1. The B pulse will then appear on the lower cathode ray trace and a variable index marker may now be located under the B pulse, this being done shift circuits. The apparatus is then switched to a #2 'fast-sweep operation position so that the trol circuit is provided for this purpose.

A and B pulses appear on two fast-sweep traces, respectively. The starting time of the fast-sweep trace on which the B pulse appears coincides with the startof the variable index marker, while the starting time of the fast-sweep trace on which the A pulse appears, coincides with the start of the slow-sweep trace. Therefore, by further adjustment of the delay circuits, the adinstable fast-sweep wave is caused to start at the proper time to bring the A and B pulses into alignment. In order to insure exact alignment, the A and B pulses should be made 'to have the same amplitude, and an amplitude balance con- After these adjustments have been made the time difference between the starts of the fast sweeps will exactly equal the time difference between the A and B pulses from the transmitters.

The present invention Aprovides an improved method and system whereby this time dlierence may be determined accurately from the readings of counters that are mechanically coupled to the same repetition period as that of the pulses bet5 several delay or phase shift circuits. respectively.

The readings of the three counters are in thousands, hundreds, and microsecond units.

The present invention is an improvement in certain respects over copending application Serial in part, in the elimination of a keyed oscillator;y

specifically, in the examples described the kc. keyed oscillator of the Minneman circuit is replaced by a kc. source that supplies signal continuously. 'I'he use of the 20 kc. oscillator results in other novel design features as will be evident from the description that follows.

It may be mentioned that it was proposed to determine the time difference of the received pulses in some of the earlier navigation systems by Calibrating the delay devices -to obtain a direct reading in microseconds. It was found, however, that with the systems then avilable no precise reading could be obtained in this way. As a result, timing marks were provided so that they could be counted to determine the time difference within one or two microseconds, for example,

According to the present invention the system is so designated that a precise time difference reading may be taken directly from the delay or phase shift circuits. The design includes the use of a sine wave phase shifter that can be calibrated accurately in microseconds, and the use of pulse selecting circuits to which gating pulses are applied under the control of calibrated delay circuits, the entire combination having various important features that will be described hereinafter.

An object of the present invention is to provide an improved method of and means for determining the time difference between electrical pulses.

A further object of the invention is to provide improved receiving equipment for a radio navigation system vof the type utilizing the propagation of radio pulses from pairs of synchronized ground stations.

A still further object of the invention is to provide an improved method of and means for indicating the time difference between radio pulses transmitted from synchronized ground stations.

A still further object of the invention is to provide an improved method of and means for obtaining a direct reading of the time difference between radio pulses transmitted from synchronizedk ground stations.

apparatus of Figure 1 and of the received pulses A and B as they appear on the traces when they are aligned,"

Figure 7 is a view of the fast-sweep cathoderay traces on the cathode-ray tube indicator and of the received pulses A and B as they appear on the two fast-sweep traces, respectively, during the .next step in obtaining more exact alignment ot the A and B pulses,

Figure 8 is a view showing the fast-sweep traces of Figure 7 superimposed or collapsed for ythe final alignment step and showing the A and B pulses exactly aligned and superimposed, and

. Figures 9 and 10 are circuit diagrams of the horizontal deiiecting slow-sweep and fast-sweep circuits, respectively, employed in the system of Figure 1.

In the several figures, similar parts are indi cated by similar reference characters.

The pulse generator and station selection circuit which will now be described under the headings The Pulse generator unit and Count sub- The invention will be better understood from pair of ground radio transmitter stations of the 05 navigation system which respectively,

Figure 4 is a group of graphs which are referred to in explaining the operation of the system shown in Figure 1,'

Figure 5 is a circuit diagram of a portion of the transmit A and B pulses.

' system shown in Figure 1,

Figure 6 is a view of the slow-sweep cathoderay traces appearing on the screen end of' the traction for station selection is the same as that described and claimed in application Serial No. 552,146, now Patent No. 2,450,360, issued September 28, 1948, filed August 31, 1944, in the name of Earl Schoenfeld and entitled Timing marker and station selection apparatus.

THE PULSE GENERATOR UNIT In Figure 1, the pulse generating circuit for producing the controlling or synchronizing pulses that control the cathode-ray deflection is shown in block diagram at the top of the figure. It is shown in detail in Figure 2. Referring to Figures 1 and 2, the pulse generator comprises a crystal oscillator I0 that produces a sine wave voltage of stable frequency which in the example illustrated is 100 kilocycles per second. The frequency of the crystal oscillator output may be'increased or decreased slightly by a manual adjustment as indicated at the control knob II for obtaining a fine right or left drift of a received pulse on a cathode-ray sweep trace, the rate of drift being :low enough to be useful on fast-sweep presentaion.

The output of the crystal oscillator I0 is supplied to a 5 to 1 sine wave frequency divider 12 to provide a 20 kc. sine wave. The 20 kc. wave is supplied through an amplifier I 2a to a blocking oscillator I3 which produces pulses having a 50 microsecond repetition rate. The 20 kc. signal is also supplied over a conductor I 08 and through an amplifier |09 to a sine wave phase shifter IIJIl for producing a variable index marker as will be described hereinafter.

The 50 as. pulses from blocking oscillator I3 are applied to a frequency divider I6 of the counter type described in White Patent 2,113,011. Ii divides the frequency by two to produce 100 as. pulses. Also, an additional circuit is provided sc that the divider I6 may be made to lose a count for the purpose of obtaining a different selectec' pulse repetition period.

The divider I6 (Figure 2) comprises a counter circuit portion including an input or bucket capacitor I1, a pair of diodes I8 and I9, a storage capacitor 2l and a blocking oscillator portion 22. In addition, it includes a pair of diodes 23 and 24 associated with the storage capacitoi 2| for the purpose of making the divider I 6 lose a count upon the application of a puise from a conductor 26 leading from a station selector cathode-ray indicator tube that is included in the switching circuit Il as will be explained hereinafter. 'rae Yomlnng ananas v oscillator 22 comprises a vacuum tube 2l and a transformer 23 coupling the plate circuit to the grid circuit. The cathode circuit includes a biasing'resistor 29, bypassed by a capacitor 3|, and connected in series with a bleeder resistor 29'. A transformer 32 supplies the 100 ps. pulses from the divider |'5 to a frequencydivider 33 which also is of the type which may be made to lose one or more counts The frequencydlvider I5 operates as follows: Each of the 50 ps. pulses of positive polarity from the oscillator I3 puts a predetermined charge on Y the comparatively large capacity storage capacitor 2| as a result` o f a. pulse of current through the comparatively small bucket" capacitor I1 and through the diode I9, the capacity of the capacitor H being small enough so that capacitor I1 recelvesfull charge before the termination of an applied pulse. At the end of this current pulse, the capacitor l1 is discharged to ground potential through the diode IB. The next 50 ns. pulse puts an additional current pulse into capacitor 2|, this raising the voltage across capacitor 2| sufllciently to trigger the blocking oscillator 22 whereby a pulse is produced across the transformer 25 as iswell understood in the art. The pulse thus produced is applied to the divider 33 with positive polarity. At the same time, the

' blocking oscillator 22 discharges the capacitor 2| to bring it back to ground potential.

The frequency divider 33 divides the frequency by fiveto produce 500 ps. pulses. It includes a counter portion comprising a bucket capacitor 35, a pair of diodes 31 and 39, and a storage capacitor 39. It also includes a blocking oscillator portion 4f comprising a vacuum tube 42, a feedback transformer 43, a biasing resistor 44 and a bypass capacitor 45.

As in the preceding divider I6, there is provided in the divider 33 a pair of diodes 41 and 48 for subtracting counts. In the divider 33, however, the application of a pulse from a conductor 49 will subtract one, two, threeor four counts depending upon the position of a switch arm 51 which is operated by a knob 55' as well as the right-drift switch` 95.

The 500 as. pulses are supplied to a frequency divider 52 that divides by two to produce 1000 as. pulses. The divider 52 is similar to the divider I5 with the count subtracting diodes omitted.

The 1000 ps. pulses are supplied to a frequency divider 55 that divides by five to produce 5000 ps. pulses which, in turn, are supplied to a frequencydivider 59 that divides by four to produce 20,000 as. pulses.` The dividers 55 and 59 are similar to the divider 52 except for the difference in circuit constants.

The 20,000 ps pulses may be passed through a clipping circuit 50 and supplied over'a conductor 5| to a square wave generator 55 (Figure 1) such as an Eccles-Jordan oscillator, for obtaining a square wave C (Figure 4) having a repetition period of 40,000 ps. This square wave is then passed through Aa cathode follower tube |5and from it are obtained, by means of suitable wave shapingand delay circuits described hereinafter,`

switch 01 which is sensed with the switch 54 as indicated by the broken line 93, the two switches being operated by the knob At the switch 54, alternate switch contact points are connected to the feedback conductor 25 whereby at these switch point positions the 20,000 as. pulses are fed back to the divider I5 to subtract counts. It may be desirable because of distributed or stray leakage in the switch 64 or capacitor 53 to connect the switch arm 04 to ground through a 1 megohm resistor 55 to permit charges to leak oft.

At the switch 51, the last six switch contact points are connected in pairs,'the three pairs of contact points #2-#3, #4-#5 and #ii-#7 being connected through bucket" capacitors 1I, 12, `|3, respectively, to the feedback conductor 49 which leads to the second count subtraction circuit. Thus, with switch 51 in any one of the last six positions, 20,000 us. lpulses are applied to the divider 33 to subtract counts.

The cathode ray of the-tube |29 is deflected horizontally by either a ,slow-sweep or a fastsweep deiiecting wave that is in synchronism with the 40,000 as. square wave from the Eccles- Jordan oscillator 55 (Figure l).

COUNT SUBTRACTIONS FOR STATION SELECTION Referring now more particularly to the feature of subtracting counts for the purpose of station selection, specific pulse repetition rates for a plurality of pairs of ground transmitter stations will be used by way of example to aid in explaining the operation.

It will be assumed that the first pair of ground stations transmit the A pulses with a repetition period of 40,000 ps. and transmit the B pulses with Va like repetition period; that the second pair of ground stations transmit A and B pulses having a repetition period of 39,900 ps.; that the third Apair transmits 39,800 as. pulses; that the fourth pair transmits 39,700 as. pulses, etc. It is apparent that for station selection at the receiving apparatus, the operator must be able to select corresponding repetition periods for the output of the square wave generator 65 which controls the cathode ray deflection cycle; namely.. periods of 40,000 as.; 39,900 as.; 39,800 ps., 39,700 us.; 39,600 as.; etc.

It will be noted that the several repetition periods diier from each other by 100 ps. or by integral multiples thereof, and that this corre,- sponds to repetition period differences of 50 ps. or integral multiples thereof at the output of the frequency divider chain, i. e., at the input of the clipper 50. Therefore, the desired repetition period can bev obtained by shortening the 20,000

. ns. period by 50 ps., by 100 as., by 150 lis., etc.

For example, to obtain the 39,900 ps. repetition period the switches G4 and 61 are moved to the #l switch contact points. `At this switch posi;-

tion the 20.000 as. pulses from the lead 52 are fed back by way of the "bucket capacitor 53, the

. switch 64 and the conductor 25 to the frequency A divider I5 only. Upon the occurrence of a 20,000

the desired driving or synchronizing pulses for Y 53 (Figure 2) of the first count subtraction circuit to a station selection switchV 54; they are also supplied to the second count subtraction circuit through a coupling or blocking capacitor 5 5 of large capacity to a second station selection as. pulse.it produces a pulse of current through the bucket capacitor 53 and through the diode .23 to add a charge to the storage capacitor 2|'.

At the end of the pulse, the capacitor 53 discharges through the diode 24 to its original poi tential. By properly selecting the capacity valu'e .of the bucket capacitor 53, the added charge is made equal to the charge Vwhich is added to the capacitor 2| by a. single 50 ps. pulse. Thun,

ananas the 20,000 us. pulse causes the blocking oscillator 22 to re one pulse earlier or 50 ils. sooner than it normally would whereby the desired repetition period of 19,950 ps. at the clipper 60 or 39,900 ps. at the output of the E-J oscillator 85 is obtained. It may be noted that, in the example given, each time a 20,000 as. pulse occurs, the divider I6 divides by one instead of by two.

To obtain the 39.800 11S. repetition period, the

switches 84 and 6l are moved to position #2. Now the 20,000 ps. pulses are applied through the "bucket capacitor 1| to the divider 33 and upon the occurrence of a 20,000 ps. pulse it applies a charge to the capacitor 39 through thediode 4B. At the end of the pulse the capacitor 1I discharges through the diode 41 to its original potential. The capacitor 1| is given a capacity value such that this charge applied by the 20,000 as. pulse is equal to the charge applied by a, single 100 as. pulse. Thus, upon the occurrence of a 20,000 ps. pulse the blocking oscillator 4I ilres one pulse early or 100 ps. sooner than it normally would whereby the desired repetition period of 19,900 ys. is obtained at the clipper 60 and a. repetition period of 39,800 Ils. is obtained at the output of the E-J oscillator 85. It may be noted that in the example given, the divider 33 divides by four instead of by five upon the occurrence of each 20,000 as. pulse.

To obtain the 39,700 as. repetition period, the switches 64 and 6l are moved to the #3 position, this being the switch position shown in the drawing. Now the 20,000 as. pulses are applied to both the divider i6 and the divider 33 through the switches 64 and 61 whereby both dividers lose a count. Specifically, the blocking oscillators 22 and 4| of dividers I6 and 33 nre 50 ps. and 100 as. early, respectively, or a total f` 150 us. early. Thus, the desired repetition period of 2 l9,850 Ils. or 39,700 fis. is obtained at the E-J oscillator output.

To obtain the 39,600 as. repetition period, the

switches 64 and 6l are moved to the #4 position. Again, the 20,000 as. pulses are applied to the divider 33 only, but this time through the capacitor 12 which has a capacity value such that a. 20,000 as. pulse causes the divider 33 to lose two counts, i. e., to trigger 200 ,us. early. Thus, the desired period of 2X19,800 as. or 39,600 as. is obtained at the E-J oscillator.

At the #5 switch position, the divider i6 again triggers 50 as. early and the divider 33 triggers 200 as. early, or a total of 250 as. for the two dividers. Thus, the repetition period is 19,750 as. at the input to clipper 60 or 39,500 as. at the output of the E--J oscillator 65.

At the #6 switch position, only the divider 33 receives the 20,000 as. pulses. These pulses are applied through the capacitor 13 which is adjusted to make the divider 33 lose three counts. Thus, it triggers 300 as. early to give a repetition period of 2X 19,700 as. or 39,400 ps. at the E-J oscillator output.

At the #7 switch position, both of the dividers i6 and 33 lose counts, divider I6 triggering 50 ps. early and divider 33 triggering 300 ps. early, or a total of 350 as. whereby the repetition period is 19,650 as. at the clipper 60 or 39,300 ps. at the E--J oscillator output.

It may be preferred to employ a different group of repetition periods than the group of 40,000 as., 39,900 as., etc. assumed above. By making the final divider stage 59 divide by three, for example, instead of by four, the divider chain output pulses have a repetition period of 15,000 ps.

. 8 so that a group of repetition periods of 30,000 ps., 29,900 as.. etc. may be employed. Or the divider stage 59 may be made to divide by five to'obtain a group of repetition periods of 50,000 as., 49,900 ps., etc.

In order to obtain a more rapid right "drift" of the A and B pulses in the preliminary steps of obtaining a time difference reading, it may be desirable to provide a capacitor that may be connected by a switch 96 t the coupling capacitor 66 so that by closing the `switch 96 additional counts will be lost by the divider 33. Thus, the A andB pulses may be drifted toward the right by closing the switch 96. When the switch 96 is opened the A and B. pulses stop drifting and again are stationary.

CATHODE RAY TRACE PRESENTATION Before describing that portion of the receiving v second of which (referred to as the variable in.

dex marker) is adjustable in time and determines the starting time t of the wave ,-g of the graph W. The starting time t of the variable index marker in relation to the fixed index marker may be adjusted by adjusting a sine wave phase shifter I 00 by a knob |00 and by adjusting two delay circuits |0| and |02 by knobs |01 and |02' (Figure 1), as will be explained hereinafter, for aligning the A and B pulses. Three switching positions identified as positions #1, #2 and 3 are used successively in aligning the A and B pulses. it will be understood that while the pulses A and B and their corresponding fast-sweep traces appear alternately on the cathode-ray tube screen, they appear to the eye to occur simultaneously because of persistence of vision, lag of phosphorescence of the screen or both.

As shown in Figure 4, the B pulse is the one that occurs after the mid-point of the A pulse period, and consequently the time interval, which elapses between the occurrence of a B pulse and the succeeding A pulse will be less than one half pulse interval. As will be seen in Figure 4, the start of one fast sweep Ch-z') coincides with the start of a slow trace, While the start of the other fast-sweep f-g) coincides with the variable index marker.

As already explained a momentary change of the recurrence rate will change the location of the pulses on the trace. Specifically, it is possible for the operator to locate the A pulse at the left side of the upper slow trace, which in turn will cause the B pulse to fall on the lower trace, and the variable index marker may be made to coincide with the B pulse. Therefore, when the function switch is turned to position #2, the A pulse will occur during the tra-ce described by the fixed fast-sweep deecting Wave h-z`, while the B pulse will occur during the trace described by the variable fast-sweep defiecting wave f-y.

A finer adjustment will permit the operator to align the A and B pulses so that the time elapsed between the start of the respective fast sweeps and the corresponding pulses are equal and occurs during the expanded parts of the traces, thereby providing good accuracy for de- Vsuccessively to operating positions #1, #2 and #3,

the desired time difference or time interval is read off the veeder-root counters |03, |04, and |05 (Figure 1) which indicate, respectively, microsecond umts, hundreds of microseconds, and thousands of microseconds. It will be apparent that the time interval thus obtained is the amount that the starting time t of the variable index marker has been delayed in time with respect tothe mid-periocld'VV (Figure 4) of the defiecting wave cycle in order to align the A and Bk pulses.

It may be noted that the upper fast trace h-i (illustrated inFigure 7) is produced by the first fast-sweep waveh-i of the deecting wave W. The lower fast trace f-g (Figure 7) is produced by the second fast-sweep wave f-g of the deilecting wave W.

DESCRIPTION OF CATHODE RAY TRACE lPRODUCING CIRCUITS, ETC., OF FIG. 1

Before describing in detail the means for shift-u gers on the front edges oi' the rectangular pulses f F so that the pulses G occur practically simultaneously with said iront edges. It ls evident that shifting the phase of the wave E results in a shift in the timing of the pulses G.

The pulses G are applied to a to 1 frequency divider lil to obtain the pulses H having a 250 as. repetition rate, The pulses H, in turn, are applied to a 4 to 1 frequency divider ||9 to obtain the pulses I having a 1000 as. repetition rate.

l The 1000 ps. pulses I are applied to a pulse seing the variable index marker, this means and f other portions of the receiver system as illus- Y trated in Figure 1 will be described generally.

Referring to Figure 1 and to thegraphs of Figure 4, the output of the 20,000 as, blocking osa lead 6| to the Eccles-Jordan oscillator 05 whereby it is triggered by the 20,000 #1S- pulses supplied thereto to produce a rectangular voltage wavey which appears unchanged at the output of a cathode follower tube I5 as the wave C.

To produce the fast-sweep deiiecting wave, W, the wave C is supplied over a conductor |98 to a differentiating circuit |05 to produce a pulse |05A that appears later as the lixed index marker of the wave V.

The circuit for producing the variable index marker of wave V.will now be described generally with reference'to Figures 1 and 4. It will be described in detail hereinafter with reference to the circuit diagram of Figure 5. As previously indicated, it is the Wave V that is applied to the fast-sweep deflecting circuit |22 for producing the fast sweep wave W.

General description of circuit for producing the variable indem marker lector circuit |20 where a particular 1000 ps. pulse is selected as explained hereinafter.

At this point it may be well to explain whyV `50 as., its repetition period is a submultiple of the slaveperiods of 20,000 ps., 19,950 ys., etc. Consequently, its phase relation with respect to the start of the slave period is the same whether said .slave period is 20,000 ps. or 19,950 as. or some other mutliple of the sine wave period.

50 ps. pulses G are also supplied from the blockf ing oscillator I3 over a conductor ||`I to a pulse selector circuit I i0. At the selector i8, one of the 5 0 us. pulses of wave G is selected by means of a gate pulse T (Figure 4). As explained hereinafter, the gate pulse T'shifts in 100 ps. jumps so shifter |00 which may be of the goniometer type,

which produces the pulses Ghaving a 50 microi second repetition rate. The oscillator ||3 trigas to select alternate 50 ps. pulses. The selected 50 jus. pulse is represented by the wave U and is supplied over a conductor ||9 to 'themixer |06. The mixed waves U and |05A pass through a clipper |2| and appear as the wave V which drives thefast sweep deecting circuit |22 toproduce the wave W.

By selecting a particular 50 us. pulse and by shifting the timing of the selected pulse by means of the phase shifter |00, it is possible to adjust the timing of the variable index marker precisely and to determine precisely by a direct reading what the timing is. The microseconds from 0 to 99 may be read from the counter |03 which is mechanically connected to the shaft of the phase shifter |00.

The microsecond readings in hundreds and in thousands are obtained from the counters |04 and |05 that indicate the settings of the delay circuits |02 and |0|, respectively. These delay circuits comprise part of the gate producing circuit that supplies the gate pulse T by means of which the desired 50 as. pulse is selected at I8.

Reference to the graphs of Figure 4 will show that the rst 50 ps. pulse of the wave G occurs upon the occurrence of the second pulse of the wave F. Specically, the blocking oscillator ||3 is not permitted to trigger in response to the occurrence of the first pulse of wave F with phase shifts greater than 360 degrees. The reason for thisvwill be explained hereinafter. This result is accomplished by utilizing a wave shaping circuit |25 that is referred to as a blocking oscillator delay circuit. The circuit |25 has the wave C applied to it which it converts to the wave J.

The wave J is a negative pulse of adjustable amplitude and is applied to the blocking oscillator ||3 so as to keep it blocked during the occurrence amaca:

of the rst pulse of wave F. In order to adjust` the amplitude of the pulse J as the phase of the wave F is shifted, an adjustable element of the oscillator delay circuit |26 is mechanically coupled to the rotor shaft of the phase shifter |00. This will be explained more fully with reference to Figure 5.

Referring now to the portion of the circuit that selects the desired 50 as. pulse by means of the gate pulse T, the wave C from the cathode follower I5 is supplied over a lead |26 to a clipper circuit |21a to produce the clipped wave C' unchanged in polarity. A ciipped wave of reversed polarity is then passed through a differentiator circuit |21 to produce the Wave K. The wave K is applied to the coarse delay circuit to trigger it on the positive pulse of the wave K. The delay circuit |0| in the example illustrated is a phantastron, the details of which will be described hereinafter with reference to Figure 5.

The output of the phantastron |0| is the wave L which is passed through a clipping amplifier |26 to produce the rectangular wave M. The back slope of the wave L and, therefore, the back edge of the wave M may be adjusted by means of the knob |0| to vary it overa wide timing range. The wave M is differentiated by a differentiating circuit |29 to produce the` Wave N. The positive pulse of the wave N triggers a rectangular pulse producing circuit |3| to produce a gate pulse O.

The gate pulse O is applied to the pulse selector circuit |20 where a particular 1000 as. pulse rep'resented by the wave P is selected. Any desired 1000 as. pulse may be selected by adjusting the delay circuit |0| and thereby shifting the position of the gate pulse O along its time axis. The selected pulse Pis applied over a conductor |32 to the flne delay circuit |02 which, preferably, is also a phantastron. Its outputjrepresented by the wave Q, is passed through a clipping amplifier |33 to produce the rectangular wave R. The timing of the back edge of the wave R may be adjusted by means of the knob |02 of the delay circuit |02. The wave R is differentiated byva circuit I 34 to produce the wave S which is applied to a rectangular pulse producing circuit |36. The positive pulse of wave S triggers the circuit |36 to produce the gate pulse T which is applied to the pulse selector circuit ||6.

,The gate pulse T may be shifted along its time axis by adjusting the delay circuit knob |02 so that any desired 50 ps pulse of wave G lying between successive 1000 ps. pulses of wave I may be selected. The selected 50 as. pulse is represented by the wave U and is applied over lead ||9 to the mixer |06 and the clipper |2| to produce the Description of mixer 106, etc.

Referring to Figures l and 10. the mixer cir.- cuit |06 and the clipping circuit |2| function to clip off the negative pulses of the wave |A l and to mix the remaining clipped positive pulses with the pulses U. Thus, the wave V is obtained at the output of the clipper-mixer combination. The mixer |06, which may consist of two vacuum tubes having a common anode resistor as shown variable index marker (of wave V) which determines the start of the fast sweep wave f-g.

From the foregoing it will be seen that sweep wave f-g can be adjusted or timed to align the A and B pulses by:

(1) Adjusting the knob |0| to select as. pulse,

(2) Adjusting the knob |02' to select a 50 ps. pulse, and Y (3) Adjusting the knob |00' to shift the phase of the selected 50 as, pulse.

It should be noted that an adjustment of the phase shifter |00 will vnever shift the selected 50 ps. pulse out of coincidence with the gate pulse T. The reason for this is that the gate pulse T is shifted along its time axis whenever the 50 as. pulses are shifted in phase due to the fact that the selected 1000 as. pulse is shifted in phase with the 50 ps. pulses, and due to the fact respect to the square wave C. There is no need.

in Figure 10, reverses the polarity of the pulses. The waves in the plate circuit of the mixer |06 are of equal amplitude due to operation of the tubes ina condition where grid andY plate voltageV approach equal amplitude. The width of the differentiated incoming pulses is short compared to that of the plate pulses, the lWidth, of the latter being controlled by a capacitor-resistor combination in the plate circuit and therefore being independentof the width of the incoming wave. This capacitor-resistor combination comprises a capacitor C| and the plate resistor RI.

The wave V is supplied to the fastsweep defiecting circuit |22 shown in detail in Figure 10 and described hereinafter. The narrow nega'- tive pulses of wave V produce the fast-sweep wave W having the useful defiecting portions h-i and f-g. The deflecting waves W and X are applied from the circuits |22 and ||5 through a wave selecting switch |23 and through a horizontal deflecting amplifier. |24 to thehorizontal deecting plates |36 of the cathode-ray indi- 2,445,361, issued July 20, 1948, filed April 2 0,

1945, in the names of Garrard Mountjoy, George D. Hulst, Jr., and Earl Schoenfeld and entitled Radio navigation system, the horizontal deflecting amplifier |24 may be provided with a switch (not shown) for changing the bias on the amplifier tubes when the function switch is changed fromthe slow-sweep position to the fast-sweep position and vice versa, thereby insuring optimum efficiency and undistorted gain from the amplifier tubes.

The switch l|23 has three contact points and three corresponding switch positions, referred to as operating positions, which are identified, reading clockwise, as positions #1, #2, and #3. There are four other operation position switches, described hereinafter, that likewise have these three switch positions and which are ganged with the switch |23. v

Switch |23, when in operation position #1, functions to apply the slow-sweep wave X to the horizontal deflecting plates |36 and, when in operation positions #2 and #3, functions to apply ilzlsi fast-sweep wave W to the deecting plates Production of variable index marker description of circuit diagram (Figure 5) 20| through a transformer 206 to the phase shifter |00. It will be noted that the 20 kc. wave Dis supplied to the phase shifter |00 continuously and remains in a fixed phase relation with for a keyed sine wave oscillator such as used in the previously mentioned Minneman system.

' tion to the start of the slave half cycle.

In the present system the phase shifter provides a phase shift of from 0 to '720 degrees through its operating range. The phase shifter 100 is of the goniometer type and is designed as described and claimed in copending application Serial No. 677,450, led June 18, 1946, now Patent No. 2,442,097, issued May 25, 1948, in the name of Stuart W. Seeley and entitled Electrical networks for phase Shifters. The coils 208 and 209 are the crossed stator coils of a goniometer, and the coil 211 is the rotor coil of the goniometer.

The stator or cross coils 208 and 209 are included in two branches or arms of a four branch network. The two branches include coils 209 and 208 and also include a capacitor 212 and a resistor 213 respectively.

A third branch` of the network comprises a resistor 214 which is connected in parallel with the branch 209, 212. The resistor 214 has the same resistance as resistor 213, and this resistance is equal to the reactance of vthe capacitor 212 at the frequency of the signal source.

A fourth branch of the network includes a capacitor 21B of the same value as the capacitor 212. this branch being in parallel with the branch 208, 213. l

The above described four branch network supplies current to the coil 208 that is displaced 90 degrees with respect to the current ilowing through the coil 209. For reasons set forth in the Seeley application the circuit is not adversely affected to any great extent by changes in the ambient temperature.

The phase shifted sine wave E has both positive and negative half cycles clipped by the limiter 112 to produce and pass the wave F during the negative `half cycle (the slave half cycle) only. The limiter 112 passes the wave F only during the negative half cycle of the wave C because the limiter tube 112a is biased to cut-olli' during the other half cycle (the master half cycle) by means of a square wave C' that is applied to its cathode by way of a lead 215. The wave C' is taken from the clipper 121a as will appear hereinafter.

The reason for producing the pulses of wave F only during the slave half cycle is to insure that the 250 as. and 1000 ,us. pulses, produced as described below, occur in the proper time rela- It will be noted that the i'lrst 1000 lis. pulse (wave I) always occurs 1000 microseconds after the start of the slave half cycle.

The wave F triggers the blocking oscillator 113, thus producing the 50 as. pulses G. The oscillator 113 is of a well known type having transformer feed-back coupling, shown at 211, from the anode circuit to the cathode circuit. 50 as. pulses G are supplied from the anode of the tube of oscillator 113 to the frequency divider 114. Also, 50 as. pulses G are supplied from the +B side of the primary of the transformer 211 over a conductor 1 11 to the pulse selector 118.

The oscillator delay circuit 125 for producing the wave J is a differentiating circuit consisting of a capacitor 219 and resistors 221 and 222 in series therewith. A shorting tap 223 on resistor 222 is coupled to the rotor of phase shifter 100 so that as the rst pulse of wave F is shifted to the right on the time axis, the amplitude of the pulse J is increased. The wave J is applied with negative polarity through a, resistor 224 to the grid of the tube of oscillator 113. So long as the pulse J holds this grid negative a certainv amount, the oscillator 113 will not be triggered by the wave F.

The reason for the above-described use of the pulse J is that without it the oscillator 113 might not stay locked in on the correct triggering pulse of wave F as the phase shift exceeds a 360 degree shift. That is, the blocking oscillator might jump from a lock-in on the desired pulse to a lock-in on an adjacent earlier pulse, for example the first pulse of wave F.

*"1 The frequency dividers 114 and 11G may be of In the example illustrated any suitable type. they are of the same general type employed in the timer chain of dividers (Figure 2) but with the blocking oscillators of the type using anode circuit to cathode circuit coupling. Also, certain circuit improvements will be apparent from the following description. Y'

The 5 to 1 frequency divider 114 comprises the well known counter section comprising a small capacity capacitor 226 and a large capacity storage capacitor 221. Capacitor 221 receives a certain charge through a diode section 228 each time a 50 ns. pulse occurs. At the end of the 50 ps. pulse the capacitor 226 discharges through the diode section 229. In the present 5 to 1 divider, the occurrence of the fifth 50 as. pulse raisesvthe charge on capacitor 221 to a value that triggers the blocking oscillator 231 to produce a pulse of wave H. At the same time the storage capacitor 221 is discharged through the gridcathode impedance of the blocking oscillator tube 232.

Thepoint at which the oscillator 231 triggers is determined in part by the setting of a bias tap 233, the bias being applied through a leak resistor 234.

The anode circuit of tube 232 is feed-back coupled to the cathode circuit by a transformer 236. The blocking oscillator is biased so that it is not free running, this biasing being adjustable both at the tap 233 and at a tap 231. Adjustment of the tap 231 adjusts the bias on the grid of a cathode follower tube 23B and the cathode of tube 238 assumes a like bias, thus setting the bias of the cathode of the oscillator tube 232. A cathode follower is used so as to eliminate the use of a high resistance voltage divider to control the bias of the blocking oscillator.

The input impedance of the cathode of the cathode follower tube 238 has a low resistance so that no substantial voltage can build up across the by-pass capacitor 239, which in the example illustrated has a capacity of 0.1 microfarad. Otherwise the triggering time of the oscillator 231 might vary due to some biasing voltagebeing built up across the by-pass capacitor 239 during the 20,000 as. period that the divider 114 is not producing the 50 ps. pulses.

The frequency divider 116 is similar to the divider 114 but has no bias voltage applied to the grid of the oscillator tube 241, the adjustable cathode bias controlled by the tap 242 providing suflicient adjustment. Also, it will be noted that here the cathode follower tube is omitted, the bias being applied directly from the tap 242 to the cathode of the oscillator tube 241.

The storage capacitor 243 of the counter circuit is shunted by a leak resistor 244 of 6.8 megohms in the present example. This permits any charge left on the capacitor 243 at the end of a 20,000 as. slave period (the divider keyed-on period) to leak off before the next slave period occurs. Otherwise, at the start of a keyed-on" orslave period the capacitor 243 might have a l charge on it due to the occurrence of one 250 as. pulse immediately following the triggering of the oscillator 24|, this one 250 as. pulse being the last occurring pulse in the preceding keyed-on or slave period. The resistor 234 provides a similar function in the divider ||4.

The 1000 as. pulses from the divider ||6 are supplied with negative polarity over a conductor 26| to the cathode of a vacuum tube 26.2v comprising the pulse selector |20. The gate pulse O is supplied with positive polarity to the grid of the tube 262 whereby a 1000 as. pulse P is passed by the tube 262 if the gate pulse O is made coincident therewith.

The gate pulse O is produced as follows. Some of the E-J signal C is supplied to the clipper |21a comprising an amplifier tube 263 that is driven hard enough to further square up the wave C. This squared-up Wave is applied from the anode of the tube 263 through a differentiating circuit |21 comprising a capacitor 264 and a resistor 266. The resulting wave K appears across resistor 266 and the positive pulse thereof triggers the carsemdelay phantastron llll to produce the wave L at"itso utput. It will be seen that the wave C that keys the limiter ||2 is taken off the cathode of the tube 263 by way of the lead 2|5. The cathodes of tubes 263 and ||2a are connected to a positive bias point on a voltage divider 265. *n

The phantastron |0| comprises a pentagrid tube 261, a trode 268 and a diode 269` connected as shown. The output wave L is taken 01T the l cathode of tube 268 and has a linear descending portion having a duration that is determined byY the point or tap on a control potentiometer 21| to which the cathode of the diode 269 is connected. Thus, the position of the back edge of the wave L is determined by adjusting thev knob IUI. i

The phantastron circuit isv described in Electronics for May 1946, pages 142 and 143.

' The operation of the phantastron delay circuit may be described as follows:

l. Initial conditions or stage VI .-In the static condition of the phantastron tube 261, grid No. 1 is at cathode potential and no current flows to the plate of the tube. Electron flow to the plate is blocked by grid No. 3 which is at a less positive potential than grid No. 2. This sets up a negative field between grids No. 2 and No. 3, which blocks electron flow past grid No. 3 by counteracting the accelerating positive eld from the acusan 16 set by the control potention'leterV 21|. It is important to note that as soon as the phantastron tube plate voltage drops below the level of the cathode voltage of the diode 269, the diode ceases to conduct and does not load down the phantastron plate circuit.

3. Stage II.-At the end of stage l, grid No. 3 has lost control oi' plate current iiow and control is exerted by grid No. 1 in the normal fashion. Sin-ce grid No. 1 is tied to B+, it attempts to rise exponentially toward B+ as the coupling capacitor 212 discharges. However, since grid No. 1 is now controlling plate current, the plate voltage drops and opposes the grid voltage change through the coupling capacitor. This negative feedback reduces the rate at which grid No. 1 can rise and makes the rate of change essentially linear. The linearity is also improved by the negative feedback developed across the cathode resistor 213. At the same time that grid No. 1 is rising, the cathode and grid No. 2 are rising and falling respectively, approaching the.

point at which grid No. 3 can again block plate current. Since the point at which control of plate current switches back from grid No. 1 to l grid No. 3 is fixed by the constants of the circuit,

the period during which negative feed-back produces a linear rate of fall of plate voltage is a direct function of'the starting plate voltage, set by the control potentiometer 21|. The rate at which grid No. 1 voltage rises and plate voltage falls is largely determined by the values of the grid No. 1 resistor, the coupling capacitor 212, and the amplication of the tube 261.

4. Stage III .-At the end of stage II, the cathode has risen and grid No. 2 has fallen suicathode and grid No. 1 to grid No. 2. Thereforg tube current flows to grid No. 2 under control of grid No. 1. The plate potential is set by the lcontrol potentiometer 21| connected to the plate` of tube 261 through the diode 269. The voltage drop in the high-plate resistor of tube 261 holds the plate voltage at essentially'the value to wjhich the control potentiometer is set. i

2. Stage I A positive pulse is applied to grid No. 3 so that the blocked electrons may flow past grid No. 2 to the plate. 'I'he rising plate current causes a falling plate potential which is coupled back to ,grid No. 1 via the coupling capacitor 21-2, producing regenerative feedback. This results in "a rapid reduction in plate and grid potential to the point at which a further drop would tend to cut off plate current and cause plate voltage to start rising again. This stops the regenerative action and blocks further fall in grid No. 1 voltage. The drop in plate and grid voltage and the time involved is essentially independent of the starting voltage of the plate.

ciently to permit grid No. 3 again to assume control of plate voltage. During the time that control of plate current is switching from grid No. 1 to grid No. 3, the plate current levels off and does not change appreciably as grid No. 1 continues to rise. This eliminates the negative feedback and permits grid No. l to rise more rapidly as the plate voltage fall ceases. This constitutes stage III. The duration of stage III is` fixed by the constants of the circuit and is not affected by the static plate voltage.

5. Stage IV.-At the end of stage III, grid No. 3 starts cutting off plate current ow, causing the plate voltage to rise. The rising plate voltage couples back to grid No. 1, speeding up the action and again providing positive or regenerative feedback. The cathode and -grid No. l rise rapidly to their original levels, grid No. 2 drops to its static level, and plate current, ceases to flow. This constitutesthe end of the time delay interval since the jump in cathode voltage is fused as the terminating point in the cycle. The duration of stage IV is essentially constant, fixed by imediately return to its initial static state value,

although plate current ceased to flow. This situation exists because of the stray capacitors from the plate to ground. The return of the phantastron plate voltage to its static level at the end of stage IV` is delayed only a negigible amount by the charging of tube and wiring capacitance. At the end of stage V, the circuit has returned to the'initial stage and awaits another trigger pulse.

1. Summary of phantastron operation- The time delay interval consists of stages I, II, III and IV. The duration of stages I, III, and IV Vdelay time is is small and is fixed by the constants of the circuit. The duration of stage II depends in linear fashion upon the plate voltage of the phantastron tube 261 at the start of the cycle. There is, therefore, a linear relationship between the voltage applied by the control potentiometer 21| and the total delay time. The output of the circuit is the negative, square-type voltage wave L with variable trailing edge developed at the cathode of tube 268. In general, this must be amplified and diflerentiated to obtain a variable delay pulse. An advantage of the circuit in addition to the linear relationship between control voltage and Ythe fact that it ls relatively insensitive to slight changes in supply voltage. The controlling voltages to the various tube elements are all derived from the same B+ supply and the eiect of changes in the supply is largely self-compensating.

The wave L om the phantastron is applied to the grid of the amplifying and clipping tube 228 to produce the rectangular wave M having a back edge that may be shifted along the time axis by means of the knob |0|. The wave M is passed through the transformer 229 which applies the resulting differentiated wave N to the grid of the tube 216 in the gate pulse producing circuit |3|.

The gate circuit |3| is a cathode coupled multivibratol` that goes through one cycle of operation when triggered and then is-inactive until again triggered. It comprises the tube 216 and a tube 211, the tubes having a common cathode resistor 218. The positive pulse of wave N triggers the gate circuit |3| to produce at the anode of the tube 211 the gate pulse O which is of 1000 lis. width or duration. The pulse O is then applied through a coupling capacitor 219 to the 1000 ps. pulse selector |20.

It will be evident that by operating the delay control knob 0 I the gate pulse O may be shifted in phase or timing so as to select any desired one of the 1000 as. pulses I. Such a selected pulse P is supplied through a transformer 28| and over conductors |32 to the iine delay phantastron |02.

The phantastron delay circuit |02 comprises a pentagrid tube 282, a triode 283, a diode 284 and a control potentiometer 286. The delay control knob |02' operates a 10-position switch for connecting the cathode of the diode 284 to any one of ten taps on the potentiometer 286. The circuit of the fine delay phantastron |02 is the same as that of the coarse delay phantastron ||l| except for the change in circuit constants required for producing the precise phase shift over the smaller time range through which the une delay phantastron operates.

The wave Q from the phantastron |02 is passed through an amplifier and clipper tube |33 to obtain thevrectangular wave R. The wave R is then differentiated by the transformer |34 to produce the wave S. The positive pulse of wave S triggers the circuit |36 to produce the gate pulse T. The circuit |36 is similar to the gate circuit |3| but has different circuit constants so as to produce a narrower gate pulse.

When the knob |02 of delay circuit |02 is operated to switch from one switch position to an adjacent one, the back edge of the pulse R (and, therefore, the gate pulse T) is shifted in time by 100 microseconds. Thus, the gate pulse T selects alternate 50 ps. pulses so that the selected pulses U supplied to the lead H8 have a time spacing of 100 as.

The gate pulse T is applied with positive polarity to the grid of the tube 281 of the 50 ps. pulse Cil selector H8. The 50 ps. pulses G are applied by way of conductor 2|8 to the cathode of the tube 281 with negative polarity. Thus, any desired one of the alternate 50 ys. pulses, such as the pulse U, that is spaced in time from a 1000 ps. pulse by a multiple of as. may be passed through the pulse selector ||8 by making the gate pulse T coincident with the desired 50 ps. pulse.

The pulse U is amplified by an amplifier tube 288 and supplied over conductor H9 to produce the variable index marker of the wave V as previously described.

While the course delay circuit |0| and the fine delay circuit |02 has been shown and described as phantastron circuits, it should be understood that while they are preferred circuits at the present time they may be replaced by delay multivibrators if desired. Suitable delay multivibrators are well known in the art.

The wave V is supplied both to the fast-sweep circuit |22 and tothe upper vertical deflecting plate 368 of the tube |39. The connection for supplying wave V to defie'cting plate 368 is by way of a conductor 383, a switch 350, a resistor 384, the conductor 38| and the capacitor 382.

In Figure 5, the values of certain circuit elements have been indicated, merely by Way of example, in ohms, megohms, and micro-microfarads.

The fast-sweep defiecting circuit 22 that is driven by the wave V (comprising the fixed and variable marker pulses) to produce the fastsweep wave W will now be described with reference to Figure 10.

The fast-sweep circuit Referring more specically to the circuit |22 for producing the fast-sweep wave W, as shown in Figure 10 the circuit comprises a vacuum tube 3|6 and a pulse shaping network that comprises two sections consisting of cathode resistors 33| and 332 shunted by capacitors 333 and 334, respectively, identified as network sections 3|1a and 3|1b. The shaping network further comprises a delay line section 3|1c comprising series resistors 336 and shunt capacitors 331 connected across the cathode resistor 33| and terminated in a resistor 338 and in the cathode resistor 332. The fast-sweep wave W is taken off the resistor 338 through an adjustable tap 339, the setting of which determines the amplitude of the wave W.

In operation, the capacitors of the network sections 3|1a and 3|1b are charged through the anode resistor 34| and the tube 3|6 to a certain voltage level between `successive pulses of the wave J to bring the tap 338 to the voltage e1. Upon the occurrence of each negative pulse of the wave V, the tube 3|6 is driven to cut-olf and the capacitors 333 and 334 discharge through the resistors 33| and 332, respectively. The section 3|1a comprising capacitor 333 and resistor 33| has a fast time constant whereby the discharge of capacitor 33 produces a voltage of steep slope across resistor 33|. The section 3|1a comprising capacitor 334 and resistor 332 has a slower time constant whereby the discharge of capacitor 334 produces a voltage of less slope across resistor 332. These two voltages of diierent slopes appear at the tap 338 as the sum of the two voltages with the voltage of the steeper slope slightly delayed by the delay network section 3 |1c.

The wave form of the wave W following the said slight delay is approximately logarithmic.

It should be understood that the fast-sweep wave W need not be of the wave form described /ment of the A'and'B pulses.

and, in fact, may be linear although some form of increased expansion at the left end of the Iastf sweep trace must be provided for the accuracy desired in the present embodiment of the invention. Such expansion may be obtained by employing either a logarithmic wave shape or an exponential wave shape, for example.

The above-described fast-sweep deflecting circuit is described and claimed in application Serial No. 583,255,v now Patent No. 2,463,969, issued March 8, 1949, filed March 17, 1945,.in the name of George D. Hulst and entitled Cathode ray de- :llection circuit.-

As previously noted, the starting time t of the fast-sweep wave f--g is determined by the adjustment 4of the 50 as. pulse U (and in turn by the variable index marker of`wave V)` wherebyv the start of the wave f-g may b e made to precede the received B pulse by the same amount that the start of theY wave hprecedes the received A pulse, this being the condition of alignnoted that the wave f-g is identical with the wave b-i whereby exact .alignment of the A and B pulses on the cathode-ray traces is obtained (as shown in Figure 8) whenthe above-described timing relation exists.

. An improved fast-sweep circuit decribed and. claimed in copending application Serial No. 674.184, now Patent No. 2,449,169, issued September 14, 1948, led June 4, 1946, in the names of Paul F. J. Holst and Loren R. Kirkwood and entitled Deflecting circuits, may be employed if desired. A f

\ The slow-sweep circuitv Referring more speciflcally'to the slow-sweep It should also be deiiecting circuit 115as shown in Figure 9, it

comprises a vacuum tube 318 and a network in the cathode circuit that comprises a cathode resistor 342 that has an adjustable tap 344 thereon and which is shunted by a capacitor 343. Positive bias is applied to the cathode of the tube 318 by connecting the lower end of cathode resistor 342 to .the junction point of a pair of bleeder rey sistors 319 and 320. This prevents the Vtube 318 from drawing current at the end of the saw- -tooth cycle so that flattening of the sawtooth wave is avoided. 'I'he operation is as follows: Each time one of the positive 20,000 as; pulses from the lead 61a is supplied through a, polarity reversing transformer 60a (Figure 1) anda lead 61h to the grid` of the tube 318 by wayof a coupling capacitor 321, the capacitor 3143 is charged suddenly from theanode voltage supply through the tube 313 to a certain voltage level to bring the tap au to the voltage level e2 (Figure 4).l At the end of each positive pulse, the capacitor The radio receiver The A and vB pulses from-a pair of ground sta-l tions (Figure'3) are received by a radio receiver of the superheterodyne type comprising a radio frequency amplifier indicated at 36|, a converter 362, an I.-F.-amplier 363 and a second detector andvideo frequency amplifier 364.' The A and B pulses are supplied with positive polarity over a conductor 366, a conductor 38| and a capacitor of 4the fast-sweep deiiecting-circuit |22.

332 to the upper vertical deilectlng plate 3335i Thus, the A and B pulses may be made to appear, as shown in Figures 6, 7 and 8, on the horizontal cathode-ray traces. The A and B pulses are made to appear with equal amplitude on the cathoderay tube screen by employing a dierential gain control circuit described hereinafter.

Slow-sweep and fast-sweep trace separation The slow-sweep traces a-b and c-d are sepal i ratedl as illustrated inFigure 6 while the receiver is on the #l operation position by means of the rectangular wave C (Figure 4) supplied from the cathode follower tube 15 (Figure 1) over a conducj 1 tor 369 to the-#1 contact point of a' trace separation switch 31|, and over a conductor 3'12 to vthe upper deflecting plate 368 of the cathode ray tube |33. Thus, the portion of the wave C, which is positive as it appears on the upper plate 366, holds the cathode ray deilection up a cer-A tain amount during the occurrence of the slow.-

sweep deiiectinsr wave c-d.

The fast-sweep tr es f-g and h-/ are sepai rated as illustrated in Figure 7 during the #2, operation position also by means of the rectangular Wave C. t Fast-sweep blanking Blanking is provided so that only the tracesffg and h-'z' appear on the cathode-ray screen when in the #2 and #3 fast-sweep operating positions. 'I'his blanking is provided by means of the negative portions of the wave Y as it ap- .E pears on the anode of the tube 3|6 (Figure 10) l The wave Y is supplied from the anode of tube 316 to the #2 and #3 contact points of a switch 321 whereby in the #lf2v and .#3 operation positions,

' this wave is supplied over conductors 322 and 326 to the grid 321 of the cathode-ray tube |39.

Trace brilliance control The diode 324 is provided to control the brilliance -of Ithe traces on the cathode-ray tube screen by preventing changes in bias on the cathode-ray tube grid 32'1 due J'to the application' of blanking pulses. A leak resistor 328 is connected across the diode 324 and the cathode of the diode 324 is connected to a variable bias voltage source (not shown). y

In operation, during the periods that the blanking waves are positive at the anode of the diode 324, the impedance of the diode 324 is very low.

so that its anodeis practically atthe bias potential of its cathode. Thus, regardless of the* form of thev blanking wave and regardless of whether any blanking wave is being applied, the

, voltage on the grid 32,1.of the cathode-ray tubeduring the cathode-ray. sweeps is substantiallythe voltage o'n the cathode of the diode 324.

DIFFERENTIAL GAIN CONTROL CIRCUri` i' A diil'erential gain control circuit for the R.IE".l

amplifier 361 of the radio receiver preferablyv is provided, as shown in Figure 1. for the purpose oi' keeping the amplitudes of the A and B pulses substantially alike at the receiver output.' thus facilitating the A and B pulse alignment. The gain control circuit includes a resistor 343 connected between the anodes of the two" tubes of the E-J oscillator 65. An adjustable diierential gain balance tap on resistor 343 may be moved to either side of the center thereof to decrease' the gain of the R.F. amplier 361 during either the reception of the pulse A or the pulse B. The voltage at the gain balance tap is supplied through a capacitor 344 and a resistor 346 to the anode of a diode 341 and to the #2 and #3 contact points of a differential gain control switch 348. Thus, when the receiver is on either the #2 or #3 operation position for pulse alignment on the fast sweeps, the differential gain control voltage is applied through the switch 346 and a conductor 349 to the gain control grid of an amplifier tube in the R.F. amplifier 36|.

The differential gain control operation with the receiver on either #2 or #3 operation position is as follows:

When the gain balance tap is at the center of resistor 343, no voltage wave is applied to the diode 341. When the tap is on one side of thisv center or balance position, a wave of one polarity is applied to the diode 341; when the tap is on ,fthe other side of the balance point, a wave of the opposite polarity is applied to the diode 341. The diode 341 functions to supply a negative bias during the negative half cycle following a positive cycle of an applied wave. For example. a positive half cycle causes diode current to charge capacitor 34E, and during the following negative half cycle the capacitor 346 discharges slowly through a resistor 35| connected across the diode 341 thus making the anode of diode 341 negative with respect to ground and reducing the gain of the I.F. amplifier 362 while the B pulse (or the A pulse) is being amplified.

With switch 348 on the #l operation position for pulse alignment, normal operating bias voltage -V is on the R.F. amplifier 30|.

PROCEDURE IN MAKING A TIME NIEASUREMENT The successive steps in making a measurement of the time interval between the A and B pulses from a pair of ground stations will now be described.

Alignment of A and B pulses i Position #1 .--After a particular pair of ground stations has been selected with the receiver setv on the #l operation position, the A and B pulses will appear stationary on the two traces af-b and c-d. A suitable drift switch such as switch 96 (Figure 2) or knob of oscillator I0 is operated to drift one of the pulses onto the upper trace c-d and over the fixed index marker at the left end of this trace. The other pulse will now appear on the lower trace a--b. The pulse on the trace c--d is the A pulse and the pulse on the trace a-b is the B pulse. That this istrue will be evident by referring to the graphs of Figure 4.

Next, the starting time t of the variable index marker of wave V is adjusted by operating the phase shift and delay controls |00', |0I' and |02 of the phase shifter |00 and the phantastrons |0| and |02 (Figures 1 and 5) to bring the variable index marker under the B pulse. The variable index marker is now carefully adjusted so that its position with respect to the B pulse is substantially the same as the position ofthe fixed index marker with respect to the A pulse.

Position #2.-Next, referring to Figure '7, the

` receiver is switched to the fast-sweep operation position #2 which results in the A and B pulses appearing on the traces h-i and f--y, respectively. As shown in Figure 4, the start of the variable index marker pulse of wave V determines the start of the second fast-sweep portion f-g of wave W, and the two starting practically simultaneously. By operating suitable drift switches such as ther'ight-drift switch 96 (Figure 2) or the knob of the crystal oscillator l0, the A and B pulses are drifted to the left ends of the traces where they are on the more expanded portion of thefast sweeps. They are then closely aligned as shown in Figure 7 by operating the knobs |00', |0|' and |02' of the phase shift and delay circuits.

Position #3.-The final alignment of the A and B pulses is done on operation position #3 with the two traces f-g and h-i superimposed as shown in Figure 8. The front edges of the A and B pulses are now exactly aligned (they usually differ slightly in shape) by operating the knob |00' of the phase shifter |00. The time reading can now be made from the counters |03, |04 and |05..

For example, if the counters |05, |04 and |03 read 6, 8 and 42, respectively, the reading is 6842 microseconds.

We claim as our invention:

1. In a radio system wherein periodically recurring A pulses and B pulses are received from pairs of ground stations and wherein a deflecting wave of fixed timing and a like deflecting Wave of adjustable timing are to be produced for defiecting the cathode ray of a cathode ray tube indicator, said A pulses having the same repetition period as said B pulses, said repetition 'period being different foreach pair of ground stations, means including an oscillator followed by a chain of frequency dividers for producing a square Wave having the same repetition period as that of the A and B pulses received from a particular pair of ground stations, the half cycle of said square wave that occurs during the occurrence of a B pulse being identified as the slave period, means for obtaining from said last means a. continuous sine wave signal having a fixed phase with respect to said slave period for any of said ground station repetition rates, a phase shifter through which said sine wave signal is passed to obtain a phase-shifted wave, means for converting said phase-shifted -wave to short-duration timing pulses, meansv for selecting a-desired one of said timing pulses, and means for producing said adjustable deiiecting wave in response to the occurrence of said selected pulse whereby said adjustable deflecting wave may be shifted to a desired Vposition along a time axis by selecting a desired timing pulse and by shifting the phase of the selected timing pulse by said phase shifter.

2. In a radio system wherein periodically recurring A pulses and B pulses are received from pairs of ground stations and wherein a deflecting wave of xed timing and a like deiiecting wave of adjustable timing are to be produced for deflecting the cathode ray of a cathode ray tube indicator, said A pulses having the same repetition period as said'B pulses, said repetition period being dierent for each pair of ground stations, means including an oscillator followed by a chain of frequency dividers for producing triggering or driving pulses having the same repetition period as that of the A and B pulses received from a particular pair of ground stations, means for causing said triggering or driving pulses to produce square waves having said same repetition period, the half cycle of said square wave that occurs during the occurrence of a B pulse being identied as the slave period, means for obtaining from said triggering pulse producing means a continuous sine wave signal having a fixed phase with respect to said slave period for any of said ground station repetition rates, a. phase shifter through which said sine wave signal is passed to obtain a phase-shifted wave, means for converting said phase-shifted, wave to short-duration timing pulses which areproduced only during said slave period, means for selecting a desired one of said timing pulses, and means for producing said adjustable deflecting wave in response to the loc currence of said selected pulse whereby said adjustable deflecting wave may be shifted t a desired position along a time axis by selecting a desired timing pulse andby shifting the phase of the selected timing pulse by said phase shifter.

3. In a radio system wherein periodically recurring A pulses and B pulses are received from pairs of ground stations and whereina defiecting wave of fixed timing and a like deecting wave of adjustable timing are to be produced for defiecting the cathode ray of a cathode ray tube indicator, said A pulses having the same repetition period as said B pulses, said repetition period being different for each pair of ground stations, means including an oscillator followed by a chain of frequency dividers for producing triggering or driving pulses having the same repetition period as that of the A and B pulses received from a particular pair of ground stations, means for causing saidtriggering or driving pulses to produce square waves having said same repetition period, the half cycle of said square wave that occurs during the occurrence of a B pulse being identified as the slave period, means for obtaining from said triggering pulse producing means a continuous sine Wave signal having a fixed phase with respect to said slave period for any of said ground station repetition rates, a phase shifter through which said sine'wave signal is passed to obtain a phase-shifted wave, means for converting said phase-shifted wave to 4short-duration timing pulses, means for producing submultiple frequency timing pulses from said rst timing pulses, means for selecting a desired submultiple pulse and means for utilizing said selected submultiple pulse for selecting a desired one of said first timing pulses, and means for producing said adjustable deflecting wave in response-to the occurrence of said'selected iirst timing pulse whereby said adjustable defiecting wave may be shifted to a desired position along a time axis by selecting a desired timing pulse and by shifting the phase of the selected timing pulse by said phase shifter,

4. In la radio system vwherein periodically recurring A pulses and B pulses are received from pairs of ground stations andwhereina defiecting wave of fixed timing and a like detlecting wave of adjustable timing are to be produced for defiecting the cathode ray of a cathode ray tube indicator, said A pulses having the same repetition period as said B pulses. said repetition period being different for each vpair 'of ground stations, means including an oscillator followed by a chain of frequency dividers for producing a square wave having the same repetition period as that of the A and B pulses received from a particular pair of lground stations, the half cycle of said Asquare wave that occurs during the occurrence of a B pulse beingfidentied as the slave period, means for obtaining from said last means a continuous sine wave signal having a fixed phase with respect to said slave period for any of said ground station repetition rates, a phase shifter through which said sine wave signal is passed to obtain a phase-shifted wave, means for converting said phase-shifted waveto short-duration A timing pulses that occur only during said slave period,

, wave in response to the occurrence of said selected 24 means for producing submultiple frequency tlming pulses from said first timing pulses, means for selecting a desired submultiple pulse and means for utilizing said selected submultiple pulse for selecting a desired one of said first timing pulses, and means for producing said adjustable deflecting Wave in response to the occurrence of said selected `first timing pulse whereby said adjustable deecting wave may be shifted to a desired position along a time axis by selecting a. desired .timing pulse and by shifting the phase of the selected timing pulse by said phase shifter.

5. In a radio system wherein periodically recurring A pulses and B pulses are received from pairs of ground stations and wherein a deflecting wave of fixed timing and a like defiecting wave of adjustable timing are to be produced for deflecting the cathode ray of a cathode ray tube indicator, said A pulses having the same repetition period as said B pulses, said repetition period being different for each pair of ground stations, certain of said repetition periods being characterized in that a half cycle or half period is an odd multiple of a certain time period, means for producing a square wave having the same repetition period as that of the received A and B pulses from a particular pair of ground stations, the half cycle of said square wave that occurs during the occurrence of a B pulse being identified as the slave period, means for producing a continuous sine wave signal having a fixed phase -with respectto said slave period and having a repetition period equal to said certain time period, a phase shifter through which said sine wave signal is passed to obtain a phase-shifted wave, means forhconverting said phase-shifted wave vto short-duration timing pulses, means for selecting a desired one of said timing pulses, and' means for producing said adjustable defiecting wave in response to the occurrence of said selected pulse whereby said adjustable deiiecting wave may be shifted to a desired position along a time axis by selecting a desired timing pulse and by shifting the phase of the selected /timing pulse by said phase shifter.

6. In a radio system wherein periodically recurring A pulses and B pulses are received from pairs of ground stations and wherein a deflecting wave of fixed timing and a like deflecting wave of adjustable timing are to be produced for deflecting the cathode ray of a cathode ray tube indicator, said A pulses having the same repetition period as said B pulses, said repetition period being' different for each pair ofground stations, certainI of said repetition periods being characterized in that a half cycle or half. period is an odd multiple of 50 microseconds, means for producing a square wave having the same repetition period as that of the received A and B pulses from a particular pair of ground stations. the half cycle of said square wave that occurs during the occurrence of a B pulse beingA identied as the slave period, means `for producing a continuous sine wave signal having a fixed phase with respect to said slave period and having a repetition period of 50 'microsecondaa phase shifter through which said sine wave signal is passed to obtain a phase-shifted wave,vmeans for converting said phase-shifted wave Ato short-duration timing pulses, means for selecting a desired one of said timing pulses, said last means including means for selecting only alternate timing pulses, and means for producing said adjustable defiecting pulse whereby said adjustable deiiecting wave may be shifted to a desired position along a time axis by selecting a desired timing pulse and by shifting the phase of the selected timing pulse by said phase shifter. l

f'1. In a radio receiving system for measuring the time interval between two received radio pulses A and B, the A pulse being transmitted at a periodic rate from a master ground station and the B pulse being transmitted at said periodic rate-from a slave ground station, means for producing a square wave having the same repetition period as said A and B pulses and having a master half cycle or period that occurs during the reception of said A pulse and having a slave half cycle or period that occurs during the reception of said B pulse, means including a source of continuous sine wave signal followed by a freduency Vdivider 'chain for producing timing pulses having a certain repetition rate, said source of sine wave signal being locked in with said square wave, means for obtaining from said divider chain other timing pulses having a repetition rate that is a submultiple of said first pulse repetition rate, means for making said divider chain active to produce pulses only during and in response to the occurrence of said slave period, a pulse selector circuit to which said submultipleV rate pulses are applied, variable delay means for producing a gate pulse that is applied to said selector circuit for selecting a desired one of such submultiple rate pulses. a second pulse selector circuit to which said first timing pulses are applied, a second variable delay means to which said one selected submultiple rate pulse is applied and comprising means for producing a pulse having a front edge that occurs in response to the occurrence of said one selected pulse and having a back edge that is adjustable in timing, means for producing a second gate pulse in response to the occurrence of said adjustable back edge, means for applying said second gate to said second pulse selector for selecting a desired one of said rst timing pulses, means for simultaneously varying the phase or timing of said selected first timing pulse and said selected submultiple rate pulse, a cathode ray tubehaving a screen, a deflecting wave generator for produc'- ing a pair of deilecting waves which are applied to said tube to produce a pair of cathode-ray traces on said screen, means for applying said A and B pulses to said cathode ray tube whereby they appear on said two traces, respectively, means for producing one of said deflecting Waves in a certain time relation to the start of said master period, and means foi-'producing the other of said deecting waves in response to the occurrence of said selected first timing pulse whereby the timing of said other deecting wave may be adjusted to bring the A and B pulses appearing on said two traces into alignment.

8. In a radio receiving system for measuring the time interval between two received radio pulses A and B having a selected repetition period, the A pulse being transmitted at a periodic rate from a master ground station and the B pulse being transmitted atsaid periodic rate from a slave ground station, the half cycle period of said A and B pulses being an odd multiple of a certain time period, means for producing a square wave having the same repetition period as said A and B pulses and having a master half cycle or period that occurs during the reception of said A pulse and having a slave half cycle or period that occurs during the reception of said B pulse, means including a source of continuous sine wave signal followed by a frequency divider chain for prodlic .in with said square wave. means for obtaining [rom said divider chain other pulses having a repetition period that is equal to said certain time period and that is a submultiple of said rst tim# ing pulse repetition period, meansl or making said divider chain active to produce pulses only during and in response to the occurrence of said slave period, a pulse selector circuit to which said first pulses are applied, variable delay Vmeans for producing a gate pulse that is applied to said selector circuit for selecting a desired oneA of said first pulses, a second pulse selector circuit to which said submultiple period pulses are applied, a second variable delay means to which said one se- "lected' pulse is applied and comprising means for producing a pulse having a front edge that occurs in response to the occurrence of said one selected pulse and having a .back'edge that is adjustable in timing, means for producing a second gate pulse in response to the occurrence of said adjustable back edge, means for applying said Vsecond gate to said second pulse selector for selecting a desired one of said submultiple period pulses, means lfor simultaneously varying the phase or timing of said selected irst pulse and said selected submultiple pulse, a cathode ray tube having a screen, a deiiecting wave generator for producing a pair of deilecting waves which are applied to said tube to produce a pair of cathoderay traces on said screen, means for applying said A and B pulses to said cathode ray tube whereby they appear on said two traces, respectively, means for producing one of said deiiecting waves in a certain time relation to the start of said master period, and means for producing the other of said deflecting waves in response to the occurs rence of said selected submultiple pulse whereby the timing of said other deflecting wave may be adjusted to bring the A and B pulses appearing on said two traces into alignment.

v9. In aradio receiving system for measuring the tim"interva1 between two received radio pulses A and B having a selected repetition rate, the A pulse being transmitted from a master ground station and the B pulse being transmitted from a slave ground station, the half cycle period of said A and B pulses being an odd multiple of 50 microseconds, means for producing a square wave having the same repetition period as said A and B pulses and having a master half cycle or period that occurs during the reception of said A pulse and having a slave half cycle or period that occurs during the reception of said B pulse, a source of sine wave signal that has a xed phase relation with respect to said square Wave and that has a repetition period of 50 microseconds, a sine wave phase shifter to which said sine wave signal is applied, a frequency divider chain supplied from said phase shifter for producing pulses having a 1000 microsecond repetition period, means for applying said square wave to said divider chain to make it active only in response to and during said slave period whereby said 1000 microsecond period pulses always occur in a definite time relation to the start of said slave period, a pulse selector to which said 1000 microsecond period pulses are applied, variable delay means for supplying a variable gate pulse to said pulse selector for selecting a desired 1000 microsecond period pulse, a second variable delay means to which said selected 1000 microsecond period pulse is applied, said second 27 delay means comprising means for producing a gate control pulse in response to the occurrence of said applied 1000 microsecond period pulse,

`means for varying the timing of the back edge oi said gate control pulse, means for producing a second variable gate pulse in response to the occurrence of said variable back edge, a second pulse selector circuit to which said second gate pulse is applied, means for supplying to said second pulse selector pulses from said frequency divider chain which have a repetition period of 50 microseconds whereby a 50 microsecond pulse may be selected Y by varying the timing of said second gate pulse,

means for varying the phase or timing of said selected 50 microsecond pulse, a cathode ray tube having a screen, a -defiecting wave generator for producing a pair of deflecting waves which are applied to said tube to produce a pair of cathoderay traces on said screen, means for applying said A and B pulses to said cathode ray tube whereby they appear on said two traces, respectively, means for producing one of said deiiecting waves in a certain time relation to the start of said master period. and means for producing the other oi' said deilecting waves in response to the occurrence oi' said selected 50 microsecond pulse whereby the timing of said other deiecting wave y may be adjusted to bring the A and B pulses appearing on said two traces into alignment.

JOHN T. MCLAMORE. MILTON J. MINNEMAN. TED E. DUNN.

REFERENCES CITED TheA following references are of record in the ille ot this patent:

UNITED STATES PATENTS OTHER REFERENCES Electronic Industries, March 1946, pp 84-93, 126. 128, 130 and 132. 

